Direct current flows in only one direction in a circuit, from the negative terminal of the voltage source to the positive. A common source of direct current (DC) is a battery. The three most common types of batteries are dry cell (used in small devices like TV remotes), wet cell (used for cars), and deep-cycle (storage batteries used primarily for backup and emergency power).

Conductors are elements that allow electrons to flow freely. Their valence shell is less than half full of electrons that are able to move easily from one atom to another.

Connecting the 6 batteries in series multiplies their voltage while keeping their current the same yielding a 36V 5A configuration. Connecting the 6 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 6V 30A configuration. Using a series-parallel connection, 3 batteries can be connected in series and 3 can be connected in parallel resulting in a 18V 15A configuration.

As their names indicate, a step-up transformer is used to step up or increase voltage and a step-down transformer is used to step down or decrease voltage. In a step-up transformer, the secondary voltage is higher than the primary voltage and it has more turns in the secondary winding than in the primary winding.

In the NM cable used for wiring homes, each cable has three wires inside a sheath with each wire covered in a different color of insulation to indicate its type. The wire with the black insulation is the 'hot' wire, white is the neutral wire, and the ground wire is either covered in green insulation or left bare.